In many contexts, both commercial and scientific, it is important to create an image on a surface, where the image contains as much information as possible. In this context, images can comprise, for example, photographically produced images of real objects and artificially generated images where information is represented by structures of varying blackness. In addition to the information, which is directly visible from the varying blackness over the image, it can be of use to add information to the image that is not directly apparent from the structures of varying blackness.
In U.S. Pat. No. 5,315,098 methods and means are illustrated which encode digital data in the angular orientation of circularly asymmetric halftone dot patterns that are written into the halftone cells of digital halftone images.
A drawback of the invention presented in U.S. Pat. No. 5,315,098 is that its use is restricted to applications where the halftone cells are of constant spatial extension across an image. Another restriction is that the halftone information in the cells is restricted in spatial extent in that it must have an elongated shape. This means that each halftone cell must contain an empty area thus reducing the overall dynamic range of the image.
It is also of importance to be able to read and interpret this information in the images applied to the surface, by means of reading apparatus. Examples can extend from applying and reading images on paper surfaces to applying and reading information from surfaces on products such as containers etc.